Method for removing organic compound by ultraviolet radiation and apparatus therefor

ABSTRACT

An organic polymer film can be completely decomposed and removed from a substrate surface by exposing the film to ultraviolet radiation having a wavelength of 180 nm or less. Also, ultraviolet radiation not longer than 180 nm in wavelength is scarcely transmitted through a transparent conductive oxide such as ITO and, thus, can be used for eliminating a defective polyimide alignment film formed on a color filter substrate and an array substrate having a transparent electrode pattern of ITO formed on the surface of a pigment portion and a TFT structure, respectively. According to the present invention, the defective alignment film on the substrates can be removed completely without any damage such as discoloring of the pigment portion and/or changing the TFT characteristics.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of removing an organicpolymer film, particularly, to a simple and convenient method ofcompletely removing a polyimide film as an alignment film in themanufacture of a color filter substrate used in a liquid crystal displaydevice. It is absolutely necessary to remove completely the polyimidefilm for the rework of a color filter substrate. And also, the presentinvention relates to a method of removing an organic polymer film on anarray substrate.

[0003] 2. Description of the Related Art

[0004] The manufacturing process of a cell of a liquid crystal displaydevice includes the step of forming an organic polymer film serving toorient liquid crystal molecules followed by forming a color filterstructure or an array structure on a substrate. The organic polymer filmincludes a film of, for example, polyimide resin (PI) and polyvinylalcohol (PVA), and is formed on the entire surface of the substrate by aprinting method or a spin coating method. Then, the film is baked,followed by applying an aligning process such as rubbing to the bakedfilm so as to form an alignment film. However, where a defect isincluded in the organic polymer film thus formed, the entire substratewas discarded as a defective substrate. Since the substrate including acolor filter structure or an array structure is prepared by employing amanufacturing technology of a very high level in order to achieve a highdensity and a high precision in a display device, the discarding of theentire substrate, which is defective, leads to an increasedmanufacturing cost.

[0005] In order to improve the situation, it is attempted to once removethe defective film of the organic polymer, followed by newly forming asatisfactory film. As the technique to remove the organic polymer film,some methods now in use for removing a photoresist film in themanufacturing process of a semiconductor device and the like, areapplicable. For example, a wet etching is one of the well-known methodfor removing an organic polymer film in which the organic polymer filmis dissolved in an appropriate solvent. In the case of a polyimide film,-butyrolactone, N-methyl pyrrolidone (NMP), etc. are used as thesolvent. Even in the case of using such a solvent, it is impossible toremove completely the residual polyimide, with the result that apolyimide film having a thickness of about 10 to 100 is left unremovedon the substrate. Also known is a dry etching method such as a plasmaetching method or an ozone ashing method. It may be possible to achievethe complete removal of the residual polyimide film by employing thesedry etching methods. However, the dry etching method requires a vacuumapparatus and an exclusive ozone generator. In other words, a relativelycostly and complex apparatus and manufacturing step is required in thedry etching method, compared with the other method. Such being thesituation, the dry etching method has not yet been put to practical use.The dry etching method gives rise to an additional difficulty.Specifically, it is necessary to rotate or rock the substrate, making itdifficult to deal with substrates of various sizes, particularly, alarge substrate sized at 600×720 mm.

[0006] Japanese Patent Disclosure (Kokai) No. 6-202111 discloses amethod of removing a polyimide liquid crystal alignment film. It isdisclosed that the film is exposed to ultraviolet radiation having awavelength of 230 to 300 nm, followed by dipping the film in a polarsolvent or an alkaline solvent. However, it has been found that theultraviolet radiation having a wavelength of 230 to 300 nm istransmitted through the underlying transparent conductive film of ITO(Indium-Tin-Oxide), though the transmission is only several percent, soas to do damage to the pigment contained in the color filter positionedbelow the ITO film. For example, discoloring is brought about in thepigment.

[0007] Also, it has been found that it is impossible to removecompletely the polyimide film by only exposure to ultraviolet radiationhaving a wavelength of 230 to 300 nm.

[0008] As described above, it is unavoidable for an organic polymer filmon a substrate for a cell of a liquid crystal display device to bear adefect caused by a defective printing or by a damage done during thealigning process such as rubbing. However, it was impossible to removecompletely the organic polymer film for reworking the substrate. It isof high importance to develop a cheap and simple method for removingcompletely the organic polymer film such as a polyimide film attached tothe substrate in order to improve the manufacturing yield and to reducethe manufacturing cost of the liquid crystal display device.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide a simple andconvenient method of completely removing an organic polymer film on asubstrate.

[0010] Another object of the present invention is to provide a simpleand convenient method of completely removing a polyimide film used as analignment film but being defective in the manufacture of a color filtersubstrate and an array substrate for a liquid crystal display device.The complete removal of the defective polyimide film is absolutelynecessary for the reworking of the substrate. It follows that anadditional object of the present invention is to provide a method whichpermits improving the manufacturing yield of a cell of a liquid crystaldisplay device.

[0011] Still another object of the present invention is to provide asimple and convenient apparatus for completely removing an organicpolymer film on a substrate.

[0012] According to the present invention, an organic polymer film,which is to be removed from a substrate surface, is exposed toultraviolet radiation having a wavelength of 180 nm or less so as todecompose and remove the organic polymer film. This particular removingmethod is useful for removing an alignment film comprising an organicpolymer such as polyimide to rework the substrate.

[0013] The principle of the removing method is shown in FIG. 1. To bemore specific, the film is considered to be removed by a breakingfunction, that is, each bond of organic polymer in the film is broken bythe energy of the irradiated ultraviolet radiation, and by an oxidizingfunction performed by oxygen within the air atmosphere, which is excitedby the energy of the ultraviolet radiation. In general, the couplingenergy (eV/molecule) between adjacent atoms contained in an organicmolecule is mainly: C—N bond (3.02); C—C bond (3.60); C—H bond (4.29);and C═C-bond (6.29). The energy (E) of the ultraviolet radiation isdetermined by:

E=hc/eλ

[0014] where h represents the Planck's constant (6.626×10⁻³⁴ [J-sec]), crepresents the speed of light (2.998×10⁸ [m/sec]), e represents theenergy of a single electron (1.602×10⁻¹⁹ [J/eV]), and 2 represents thewavelength of the light [m]. The energy of the ultraviolet radiationemitted from a conventional low pressure mercury lamp having an outputwavelength of 254 nm is 4.88 eV, which is smaller than the couplingenergy of the C═C bond noted above. In other words, it is impossible forthe ultraviolet radiation having a wavelength of 254 nm to break the C═Cbond. It follows that the pyromellitic acid portion and the condensedring portion of the polyimide structure given below are not decomposedbut remain on the substrate:

[0015] On the other hand, ultraviolet radiation having a wavelength of180 nm is capable of imparting an energy of 6.89 eV that is large enoughto break the C═C bond. Therefore, the interatomic bonds included inalmost all the organic polymer or molecule can be broken and thus theorganic polymer or molecule can be decomposed.

[0016] Also, the oxygen molecules within the atmosphere generate excitedoxygen atoms O* when exposed to ultraviolet radiation as shown below:

[0017] The excited oxygen atom O* readily reacts with each of the atomsand atomic groups broken by irradiation of the ultraviolet radiation andconvert atoms of C, N and H into molecules of CO₂, NO_(x) and H₂O. Thesemolecules are gaseous and, thus, can be moved from the substrate intothe atmosphere. It follows that these gaseous molecules can be removedeasily by discharging the atmosphere from within the chamber.Alternatively, the excited oxygen atom is considered to attack directlythe organic polymer so as to oxidize the particular material and, thus,to generate the similar gaseous oxide molecules.

[0018] However, the high energy of the ultraviolet radiation having awavelength shorter than 180 nm may do damage to the substrate. Forexample, it is possible for the particular ultraviolet radiation todecompose even the useful material contained in the structure below thefilm of the organic polymer. For example, if the pigment portion isexposed directly to ultraviolet radiation in the color filter substrateincluded in a liquid crystal display device, the pigment portion suffersfrom a damage such as discoloring. It should be noted in this connectionthat a transparent electrode pattern made of ITO or IZO(Indium-Zinc-Oxide) is formed on the surface of the pigment portion inthe ordinary color filter substrate. It has been found, however, thatultraviolet radiation having a wavelength not longer than 180 nm isscarcely transmitted through the particular transparent electrodepattern, with the result that the particular electrode pattern acts as aprotective film of the pigment portion. Thus the method of the presentinvention makes it possible to remove easily the polyimide alignmentfilm on a substrate including a color filter structure.

[0019] On the other hand, the typical array structure as shown in FIG.4(a) for a liquid crystal display device is adversely effected by thedirectly exposure to ultraviolet radiation, transistor characteristicsof the semiconductor layer are shifted, and electrification will beoccurred in the gate insulating layer. In particular, TFTcharacteristics are changed such as that the gate threshold voltage isdecreased and that the drain off current is increased. As the result,maintaining the charge at the TFT is leaked to make a white spot on thedisplay and to lead a poor display quality. However, an array structurehaving a polymer film on the array (it is called as PFA structure or PFAsubstrate, hereafter) as shown in FIG. 4(b) which has a ITO or IZO filmon the surface of the TFT element may avoid the damage by exposure tothe ultraviolet radiation, because the lower semiconductor layer can beprotected by the ITO or IZO film. This PFA structure is developed inorder to increase the aperture ratio by the structure having atransparent electrically conductive film which acts a role of a gateline, on the TFT structure through an organic insulating layer.Therefore, the removing of the polyimide alignment film on the substratehaving PFA structure is easily achieved by the present invention.

[0020] The thickness of the ITO or IZO film formed on these substratesis approximately 1500 angstrom to maintain the high transparency in thevisible light but it is sufficient to shield the ultraviolet radiationhaving a wavelength of 180 nm or less.

[0021] Furthermore, in light of the above principle, it is easilyunderstood that the object to be decomposed and removed is not onlypolymer but also any organic molecules. An example of such organicmolecules is a contamination attached on the substrates duringmanufacturing process. Thus, the removing method and the apparatus canbe applied to removing a residue of resist composition, a residue aftertypical cleaning and a surface contamination in the manufacturingprocess for not only LCD but also microelectronics or semiconductordevice.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 shows the principle utilized in the present invention.

[0023]FIG. 2 schematically shows a removing apparatus adapted to workthe present invention.

[0024]FIG. 3 is a cross sectional view schematically showing thestructure of a color filter substrate.

[0025]FIG. 4 is a cross sectional view schematically showing thestructure of an array substrates, which are (a) a conventional structureof TFT array substrate without a polymer film and a transparentelectrode and (b) a PFA structure of TFT array substrate having apolymer film and a transparent electrode.

[0026]FIG. 5 shows spectra denoting the surface XPS analytical result ofa color filter substrate which is being removed the polyimide filmthereon in accordance with the present invention, showing the cases of(a) before exposing to ultraviolet radiation, and (b) after exposing tothe ultraviolet radiation.

[0027]FIG. 6 shows graphs denoting the relation between the gate voltageand the drain current which shows the change of the TFT characteristicsbetween before and after exposure to the ultraviolet radiation having awavelength of 172 nm for (a) the array substrate structure with an ITOfilm and a polymer film, and for (b) the array substrate structurewithout an ITO film and an polymer film.

[0028] In the present invention, a film of an organic polymer on asubstrate, which should be removed, is exposed to ultraviolet radiationhaving a wavelength of 180 nm or less to decompose and remove the filmof the organic polymer.

[0029]FIG. 2 schematically shows an apparatus 100 for working thepresent invention. The apparatus 100 comprises a chamber 101. As shownin the drawing, arranged within the chamber 101 are ultravioletradiation emitting device 110, an exposing stage 120 on which asubstrate 50 is mounted so as to permit the substrate 50 to be locatedat an exposing position, an ozone filter 130 for removing with safetythe ozone O₃ generated by the ultraviolet radiation irradiation, and anozone sensor 140. Further, it is desirable to arrange within the chamber101 a transfer conveyor 150 for transferring the substrate bearing afilm of an organic polymer or an organic compound to be removed into thechamber 101 and another transfer conveyor 160 for transferring thesubstrate having the film of the organic polymer or the organic compoundremoved therefrom out of the chamber 101. It is also desirable toarrange, optionally, within the chamber 101 a monitor 170 adapted tomonitor the completion of the removal of the organic polymer film or theorganic compound.

[0030] The ultraviolet radiation emitting device 110 useful in thepresent invention emits only ultraviolet radiation having a wavelengthof 180 nm or less. The output power of the device 110, which depends onthe kind and thickness of the organic polymer film or the organiccompound to be removed, should be at least about 4 mW/cm², preferably atleast about 8 mW/cm². The ultraviolet radiation emitting device meetingthe particular condition includes, for example, an “Excimer Lamp” (tradename) available from Ushio Denki K. K. (Otemachi 2-6-1, Chiyoda-ku,Tokyo) and Hoya Shot K. K. (Shinjuku 3-23-7, Shinjuku-ku, Tokyo). TheExcimer Lamp emits ultraviolet radiation having a wavelength of 172 nmwith an output power of 4 to 30 mW/cm². In addition, it is also possibleto use a D2 lamp (deuterium lamp), an argon lamp, a krypton lamp, etc.

[0031] As shown in chemical formula 2 given previously, the oxygenmolecules within the atmosphere of the chamber generates ozone togetherwith excited oxygen atoms upon exposure to ultraviolet radiation. Theultraviolet radiation having a wavelength of 172 nm which is used in thepresent invention exhibits high energy as described above. Then, it canbe seen that ozone and excited oxygen atoms are generated inconcentration over than 1000 ppm just under the ultraviolet radiationemitting device, upon emitting in an atmosphere. This ozoneconcentration is sufficient enough to remove any organic compoundusually, and an additional ozone generator will not be necessary toworking the subject invention. As known to the art, ozone is stronglypoisonous and harmful to the human body, making it necessary todecompose the ozone within the chamber so as to be converted into a safesubstance before the atmosphere within the chamber is discharged to theoutside. It follows that it is necessary to use the ozone sensor 140 formonitoring the ozone concentration within the chamber and the ozonefilter 130 for disposing of the ozone with safety. A known ozone sensorand a known ozone filter can be used in the present invention. It isalso necessary to seal sufficiently the chamber 101 in order to preventthe ozone from leaking to the outside of the chamber 101. On the otherhand, it should be noted that oxygen molecules within the atmosphere ofthe chamber 101 are consumed during removal of the organic polymer filmor the organic compound to be removed so as to increase the oxidecompounds formed by the decomposition such as CO₂, NO_(x) and H₂O,making it necessary to use a suction-discharge means (not shown) tomaintain constant the atmosphere within the chamber.

[0032] The exposing stage 120 for transferring and supporting thesubstrate and the carry in conveyor 150 and the carry out conveyor 160are known to the art. The exposing stage 120 includes an X-Y stage and aZ-stage that can be moved in the horizontal and vertical directions andcan be fixed at a suitable position for setting the exposing position.

[0033] A heater adapted to heat the substrate can be used optionally.The rate of removing the organic compound is accelerated around threetimes if the substrate is heated at a temperature of 100-120 degrees C.As the heater, hot plate or electric heating wire combined with theexposing stage in order to control the temperature at a surface of theexposing stage where the substrate is placed, may be useful. And, thechamber with a heater and a temperature controller in order to controlthe temperature in the chamber entirely may be also useful.

[0034] The monitor 170 may be, for example, of the type that irradiatesthe surface of the substrate with an electromagnetic radiation such asan infrared ray so as to obtain the information of the substrate surfaceby the spectrum of the reflected radiation or the scattered radiation,or the type that is designed to measure the concentrations within thechamber of the substances such as CO₂ and NO_(x), which are formed as aresult of decomposition of the film of the organic polymer or theorganic compound upon exposure to ultraviolet radiation. Since exposureof the substrate to an excessive amount of ultraviolet radiation maycause an undesirable damage to the substrate, it is desirable to finishthe exposure at the time when the film of the organic polymer has beenremoved completely. For that purpose, it is possible to design theapparatus to transmit a signal to the emitting device 110 to finish theemission when the monitor 170 has detected the completion of theremoval.

[0035] Instead of the monitor mentioned above, a photometer whichindicates a dose emitted by the ultraviolet emitting device can beprovided. In this situation, the exposing duration is determined by thetotal doses of the ultraviolet radiation.

[0036] The present invention is useful for particularly the reworking ofthe substrate that includes the removal of the polyimide alignment filmon the color filter substrate for a liquid crystal display device.Although manufacture of a color filter substrate is described herein asan example, it may be of no difficulty for those skilled in the art tounderstand that the technical idea of the present invention can also beapplied to the removal of a film of an organic polymer on anothersubstrate.

[0037]FIG. 3 shows the structure of a typical color filter substrate fora liquid crystal display device. As shown in the drawing, the colorfilter substrate includes a transparent substrate. A black matrix (BM)pattern and a pigment portion are formed on the substrate. Further, alayer of a transparent conductive oxide such as ITO or IZO is formed asa transparent electrode on the pigment portion. The thickness of thetransparent conductive oxide layer, which depends on the parameters suchas the conductivity and transmittance required for the color filtersubstrate, should be at least several hundred angstroms, in generalabout 1300 to 1700 Å.

[0038] An alignment film is formed on the color filter substrate. A filmof an organic polymer such as a polyimide resin is used as the alignmentfilm, which is formed on the entire surface of the substrate by printingor spin coating. The film of the organic polymer has a thickness of upto about 1000 Å, in general about 600 to about 800 Å. The film of theorganic polymer formed on the substrate surface is baked and, then, analigning process such as rubbing or an energy beam irradiation isapplied to the baked film so as to prepare an alignment film. Theresultant alignment film is carried out a visual observation by thenaked eye or an automatic optical inspecting tool to detect any defectsuch as a defective printing, an existence of a foreign matter, ascratch or peeling. Where a defect has been detected in the alignmentfilm, the color filter substrate itself including the defectivealignment film is transferred to the reworking process as a defectivesubstrate. The reworking process comprises the steps of removing thedefective alignment film from the color filter substrate and forming analignment film again.

[0039] In the present invention, the defective alignment film is removedfrom the color filter substrate by using an apparatus 100 for removing afilm of an organic polymer. In the first step, the defective substrate50 is transferred into the chamber 101. The carry in conveyor 150 can beused for transference. The transferred substrate 50 is settled to theexposing stage 120, followed by determining the horizontal position topermit the substrate 50 to be positioned within a suitable exposingrange, for instance about 5 mm or less, preferably about 1-2 mm.Further, the vertical position is determined to permit the substrate 50to be positioned at a suitable exposing distance. After the horizontaland vertical positions are finely adjusted to permit the substrate 50 tobe at a suitable exposing position, the position of the substrate 50 isfixed.

[0040] In the next step, ultraviolet radiation having a wavelength of180 nm or less is emitted from the ultraviolet radiation emitting device110 to expose the polyimide alignment film, which is the organic polymerfilm 60 to be removed, on the substrate to the ultraviolet radiation. Itis possible to carry out the exposure of the substrate 50 for a timedetermined by experience, or it is possible to finish the irradiation atthe time when the removal of the film 60 from the substrate 50 has beenconfirmed. The exposing time, which depends on the parameters such asthe kind and thickness of the organic polymer film to be removed and thewavelength and output power of the ultraviolet radiation used for theexposure, is generally of the order of several minutes to several tensminutes. For example, where a polyimide resin alignment film having athickness of about 700 Å is removed by exposing to the ultravioletradiation having a wavelength of 172 nm (light source illuminance of 8mW/cm²), the exposure is carried out for about 10 minutes to about 30minutes. The ozone generated during the ultraviolet radiationirradiation is monitored by the ozone sensor and is disposed of by theozone; filter. Also, the by-product gases formed as a result of thedecomposition of the organic polymer film are discharged out of thechamber by a suitable method.

[0041] When the ultraviolet radiation irradiation is stopped afterremoval of the defective alignment film, which is the film of an organicpolymer, from the substrate surface, the substrate 50 fixed to theexposing stage is released from the stage, followed by transferring thesubstrate 50 out of the chamber 101 by, for example, the carry outconveyor 160. The polyimide alignment film is completely removed fromthe color filter substrate after the irradiation with the ultravioletradiation, making it unnecessary to further wash or rinse the colorfilter substrate. It should also be noted that, since the pigmentportion is protected by the ITO transparent conductive film or the IZOtransparent conductive film, the pigment portion does not suffer from adamage such as discoloring. It follows that the color filter substratecan be reworked without deterioration.

[0042] The color filter substrate having the defective alignment filmcompletely removed therefrom can be reworked by newly forming analignment film thereon.

EXAMPLE 1

[0043] Prepared was a color filter substrate having ITO film formedthereon in a thickness of about 1500 Å as a transparent electrode,followed by forming a polyimide film on the ITO film in a thickness ofabout 700 Å so as to obtain a sample substrate.

[0044] The sample substrate thus obtained was exposed to ultravioletradiation having a wavelength of 172 nm (light source illuminance of 7.8mW/cm²) for 30 minuets.

[0045] The surface-of the sample substrate both before and after theexposure to ultraviolet radiation was measured by an X-ray photoelectronspectroscopy (XPS), with the result as shown in FIG. 5. Presence ofatoms of-each of C, N and 0 was recognized on the surface of the samplesubstrate before exposing, as shown in FIG. 5(a), supporting that thesubstrate surface was covered with the polyimide resin. On the otherhand, the presence of N was not recognized on the surface of the samplesubstrate after exposing. Also, the presence of In and Sn in addition toO was newly recognized after exposing, as shown in FIG. 5(b). It isconsidered reasonable to understand that the polyimide resin was removedsubstantially completely by exposing to ultraviolet radiation and theunderlying ITO film was exposed to the surface. Incidentally, the signalassigned to C, which is observed in FIG. 5(b), denotes the ordinary baselevel and differs from the signal denoting the presence of a polyimideresin.

[0046] The surface of the sample substrate after exposing was observedwith an AFM (Atomic Force Microscopy). As the result, the presence ofpolyimide resin was not recognized.

[0047] The sample substrate both before and after the ultravioletradiation irradiation was examined in respect of the opticalcharacteristics as a color filter. As the result, the transmittance andthe chromaticity before exposing were found to be retained afterexposing to ultraviolet radiation.

COMPARATIVE EXAMPLE 1

[0048] A sample substrate similar to that used in Example 1 was exposedto ultraviolet radiation having a wavelength of 254 nm for 30 minutes.In this case, a polyimide resin was found by a visual observation tohave remained on the substrate sample after exposing to the ultravioletradiation having a wavelength of 254 nm. Further, discoloration wasobserved in the pigment portion.

EXAMPLE 2

[0049] A polyimide film was newly printed as in Example 1 on the surfaceof the sample substrate prepared as in Example 1 after the irradiationwith ultraviolet radiation so as to obtain a reworked substrate. Anincomplete printing such that the newly formed polyimide film isrepelled on the surface of the sample substrate after the irradiationwith the ultraviolet radiation was not observed.

EXAMPLE 3

[0050] A liquid crystal display device was assembled by using thereworked substrate obtained in Example 2. Also, the liquid crystaldisplay device thus assembled was subjected to a thermal humiditybearing (THB) test for 300 hours under the temperature of 70° C. and therelative humidity (RH) of 80%. The display characteristics such as thedisplay fineness, brightness, gradation, contrast and view field of theassembled liquid crystal display device both before and after the THBtest were found to be substantially equal to those of a liquid crystaldisplay device prepared by using a satisfactory sample substrate whichis not a reworked substrate.

EXAMPLE 4

[0051] A sample substrate similar to that used in Example 1 was exposedto ultraviolet radiation having a wavelength of 254 nm for 10 minuteswith heating and maintaining the surface temperature of the substrate ataround 110 degrees C. As the result, the presence of polyimide resin wasnot observed on the surface of the sample substrate after exposing.

EXAMPLE 5

[0052] Prepared was a PFA substrate having an ITO film thereon in athickness of about 1500 as a transparent electrode so as to obtain asample substrate. The sample substrate was exposed to ultravioletradiation having a, wavelength of 172 nm (light source illuminance of7.8 mW/cm²) for 1 minute. The TFT characteristics of the samplesubstrate both before and after the exposure to the ultravioletradiation was evaluated by measuring the relation between gate voltageand drain current. The result is shown in FIG. 6(a). Any changes of thecharacteristics between before and after the exposure were not observed.

COMPARATIVE EXAMPLE 2

[0053] An array substrate similar to that used in Example 5 but nothaving the organic film and the ITO film was exposed to ultravioletradiation having a wavelength of 172 nm for 1 minute. The TFTcharacteristics of the array substrate without organic and ITO filmsboth before and after the exposure to the ultraviolet radiation wasevaluated by measuring the relation between gate voltage and draincurrent. As shown in FIG. 6(b), the data after exposure indicate thechanges such as lower shift of the gate threshold voltage and extremelyhigher drain off current than the data before exposure.

EXAMPLE 6

[0054] Prepared was a PFA substrate having ITO film formed thereon in athickness of about 1500 Å as a transparent electrode, followed byforming a polyimide film on the ITO film in a thickness of about 700 Åso as to obtain a sample substrate. The sample substrate thus obtainedwas exposed to ultraviolet radiation having a wavelength of 172 nm(light source illuminance of 7.8 mW/cm²) for 30 minutes. The presence ofpolyimide resin was not observed on the surface of the sample substrateafter exposed. Also, any changes of the TFT characteristics betweenbefore and after exposure were not observed.

What is claimed is:
 1. A method of removing an organic polymer film on asubstrate which comprises exposing the organic polymer film toultraviolet radiation having a wavelength of 180 nm or less.
 2. Themethod according to claim 2, wherein said organic polymer is decomposedto a volatile compound to be removed upon the exposure to saidultraviolet radiation.
 3. The method according to claim 1 or 2, whereinsaid organic polymer is oxidized by an exited oxygen generated byexposing an oxygen atom in an atmosphere to said ultraviolet radiation.4. The method according to claim 1, wherein said organic polymer film isexposed to said ultraviolet radiation with a sufficient output power fora sufficient period to decompose substantially completely the organicpolymer film.
 5. The method according to claim 1, wherein said organicpolymer film has a C═C bond.
 6. The method according to claim 5, whereinsaid organic polymer film comprises polyimide.
 7. The method accordingto claim 1, further comprising heating the substrate.
 8. The methodaccording to claim 7, wherein the temperature of said substrate is100-120 degrees C.
 9. The method according to claim 1, wherein saidsubstrate is a color filter substrate having a pigment portion having atransparent electrode pattern formed thereon.
 10. The method accordingto claim 9, wherein said transparent electrode pattern comprises amaterial selected from the group consisting of ITO and IZO.
 11. Themethod according to claim 9 or 10, wherein said organic polymer film isan alignment film.
 12. A method of manufacturing a substrate,comprising: preparing a substrate including a transparent electrodepattern formed on the surface thereof; attaching a first organic polymerfilm on said substrate; exposing said first organic polymer film toultraviolet radiation having a wavelength that is not transmittedthrough said transparent electrode pattern so as to remove said firstorganic film from said substrate; and attaching a second organic polymerfilm to the substrate from which said first organic film has beenremoved.
 13. The method according to claim 12, wherein said ultravioletradiation does not include wavelength longer than 180 nm.
 14. The methodaccording to claim 12, wherein said first organic polymer film isexposed to said ultraviolet radiation in said removing step with anoutput power of the ultraviolet radiation and the exposure time setsufficient for removing substantially completely the first organicpolymer film.
 15. The method according to claim 12, wherein said firstorganic polymer film comprises polyimide.
 16. A liquid crystal displaydevice, comprising a substrate prepared by any one of the method definedin claims 12 to
 15. 17. An apparatus for removing an organic compound ona substrate comprising: a chamber adapted to maintain a predeterminedatmosphere; a stage adapted to hold the substrate thereon; a lightsource adapted to generate ultraviolet radiation having a wavelength of180 nm or less; and an ozone filter and an ozone sensor adapted todispose of ozone generated by said ultraviolet radiation; and a heateradapted to heat the substrate.
 18. The apparatus according to claim 17,further comprising a monitor adapted to detect the substantiallycomplete removal of the organic compound film from the substrate.
 19. Amethod of removing an organic compound on an array substrate with atransparent electrically conductive film formed thereon, which comprisesexposing the organic compound to ultraviolet radiation having awavelength of 180 nm or less.